1. Field of the Invention
The invention relates to an internal combustion engine including plural cylinders, a control apparatus and a control method for an internal combustion engine including plural cylinders.
2. Description of the Related Art
A gasoline engine is proposed, which includes a variable valve system in which valve opening characteristics such as opening/closing timing and an opening/closing amount of a valve are varied. In the gasoline engine including the variable valve system, an intake air amount of each cylinder can be controlled by changing valve opening characteristics of an intake valve (refer to Japanese Patent Laid-Open Publication No. JP-A-2001-263015).
In the gasoline engine including the variable valve system, there may be irregular differences in valve opening characteristics of an intake valve among cylinders. Such differences in valve opening characteristics among cylinders cause a problem concerning the operating state of the internal combustion engine. For example, when a working angle or a lift amount is small, the differences in valve opening characteristics cause differences in the intake air amount among the cylinders. The differences in the intake air amount cause differences in the air-fuel ratio, which results in a problem such as an increase in an emission amount.
Thus, in order to obtain a desired combustion state even when there are differences in the intake air amount among the cylinders, a technology is proposed, in which a fuel injection amount for each cylinder is decided according to the intake air amount in each cylinder. As an example of such a technology, Japanese Patent Laid-Open Publication No. JP-A-11-62639 discloses a technology in which a fuel injection amount for achieving a stoichiometric air-fuel ratio (hereinafter, referred to as “basic injection amount”) is decided for each cylinder.
However, when the fuel injection amounts in all of the cylinders are controlled such that the air-fuel ratios in all of the cylinders become equal, the torque generated in each cylinder (hereinafter, referred to as “generated torque”) is different due to the fact that the intake air amount varies with each cylinder. The differences in the generated torque cause engine speed fluctuation or torque fluctuation.